1. Field of the Invention
The present invention relates to an epoxy resin composition which provides a cured product having a high glass transition point, an extremely low coefficient of expansion, good crack resistance, and low stress. More particularly, it is concerned with an epoxy resin composition suitable for use as an encapsulator for semiconductor devices.
2. Description of the Prior Art
An epoxy resin composition which is composed of a curable epoxy resin, a curing agent, and a variety of additives is used for encapsulating semiconductor devices because it is superior to other thermosetting resins in moldability, adhesion, electrical properties, mechanical properties, and moisture resistance. However, there is presently a need for it to meet new requirements arising from the recent advance in semiconductor devices. With the development of smaller and thinner electronic machines and equipment, the package of semiconductor devices has become diversified. On the other hand, the electronics technology has produced semiconductor devices in which semiconductor elements are bonded directly to a printed circuit board or heat sink. Such semiconductor devices encounter some problems when encapsulated with a conventional epoxy resin composition because of the difference in the coefficient of thermal expansion between the printed circuit board and the epoxy resin composition. The difference in the coefficient of thermal expansion exerts a great stress on the semiconductor element, resulting in cracking and deformation, which would deteriorate the performance and appearance of the element.
In order to solve this problem, an epoxy resin composition composed of a curable epoxy resin and organopolysiloxane (Japanese patent Laid-open No. 129246/1981) and an epoxy resin composition incorporated with a block copolymer composed of an aromatic polymer and organopolysiloxane (Japanese patent Laid-open No. 21417/1983), has been proposed. These epoxy resin compositions produce a lower level of stress than the conventional ones. However, there are some instances where even these new epoxy resin compositions do not meet the severe requirements for an encapsulator of sophisticated semiconductor devices. Thus there still is a demand for a new encapsulator which is more reliable and less likely to exert stress to the semiconductor element. The present invention was completed under the above-mentioned circumstance.